The SARS-Coronavirus-Host Interactome: Identification of Cyclophilins as Target for Pan-Coronavirus Inhibitors

Top Cited Papers
Open Access
Publisher Website
Google Scholar
Abstract
Coronaviruses (CoVs) are important human and animal pathogens that induce fatal respiratory, gastrointestinal and neurological disease. The outbreak of the severe acute respiratory syndrome (SARS) in 2002/2003 has demonstrated human vulnerability to (Coronavirus) CoV epidemics. Neither vaccines nor therapeutics are available against human and animal CoVs. Knowledge of host cell proteins that take part in pivotal virus-host interactions could define broad-spectrum antiviral targets. In this study, we used a systems biology approach employing a genome-wide yeast-two hybrid interaction screen to identify immunopilins (PPIA, PPIB, PPIH, PPIG, FKBP1A, FKBP1B) as interaction partners of the CoV non-structural protein 1 (Nsp1). These molecules modulate the Calcineurin/NFAT pathway that plays an important role in immune cell activation. Overexpression of NSP1 and infection with live SARS-CoV strongly increased signalling through the Calcineurin/NFAT pathway and enhanced the induction of interleukin 2, compatible with late-stage immunopathogenicity and long-term cytokine dysregulation as observed in severe SARS cases. Conversely, inhibition of cyclophilins by cyclosporine A (CspA) blocked the replication of CoVs of all genera, including SARS-CoV, human CoV-229E and -NL-63, feline CoV, as well as avian infectious bronchitis virus. Non-immunosuppressive derivatives of CspA might serve as broad-range CoV inhibitors applicable against emerging CoVs as well as ubiquitous pathogens of humans and livestock. Broad-range anti-infective drugs are well known against bacteria, fungi, and parasites. These pathogens maintain their own metabolism distinctive from that of the host. Broad-range drugs can be obtained by targeting elements that several of these organisms have in common. In contrast, target overlap between different viruses is minimal. The replication of viruses is highly interweaved with the metabolism of the host cell. A high potential in the development of antivirals with broad activity might therefore reside in the identification of host factors elemental to virus replication. In this work we followed a systems biology approach, screening for interactions between virus and host proteins by employing an automated yeast-two-hybrid setup. Upon binding of a viral protein to cyclophilins the screen led to the identification of the Calcineurin/NFAT pathway possibly being involved in the pathogenesis of SARS-Coronavirus. Secondly, cyclophilins were suggested to play an elemental role in virus replication since cyclosporin A inhibited replication of all Coronavirus prototype members tested. This large range of viruses includes common cold viruses, the SARS agent, as well as a range of animal viruses. For the first time this work shows that an undirected, systems-biology approach could identify a host-encoded, broad-range antiviral target.